Mid-Term Results of Particulated Juvenile Articular Cartilage Allograft Transplantation to the Knee

OBJECTIVES: Full-thickness chondral defects of the knee in the young, active patient remain a concerning orthopedic entity given the low capacity for natural regeneration of articular cartilage and limited established treatment options. In the knee, transplantation of particulated juvenile articular cartilage (Zimmer DeNovo NT) has been shown in small studies with only short-term outcomes to have excellent potential. This is the first study that has followed patients greater than 2 years. METHODS: All patients at a single institution who underwent a DeNovo NT cartilage transplant procedure for single or multiple lesions of the knee between 2010 and 2014 were identified. All patients had an MRI pre-operatively. Size and location of defects treated were recorded intra-operatively, as were all concomitant procedures. MRI was performed at a minimum of 6 months post-operatively. MRIs were all read by musculoskeletal radiologists and repair tissue evaluated by the MOCART (Magentic Resonance Observation of Cartilage Repair Tissue) score. All patients were administered the Lysholm questionnaire pre and postoperatively. RESULTS: 26 patients (28 knees) were identified, 17:9 M:F, and average age 33.7 years (21-49 years). A total of 34 Outerbridge grade IV cartilage lesions were treated, 10 lesions on the MFC, 6 on the LFC, 13 on the patella and 5 on the trochlea. Average cross sectional area of the lesions was 3.075 cm2; average area of MFC lesions was 2.844cm2, LFC 2.69 cm2, patellar lesions 3.795cm2, and trochlea lesions 2.195 cm2. Associated procedures included patellar realignment in 16/28 (tibial tubercle osteotomy in 12, VMO advancement in 4); 6 MPFL reconstructions and 10 lateral releases. ACL reconstruction occurred in 7/28 knees and partial meniscectomy in 9. There were 11 returns to the OR, 3 for MUA, 9 for arthroscopic debridement (including 5 hypertrophic graft tissue, 1 loose body and 2 further microfractures of a prior or new lesion). On MRIs at 6 months post-op. The average MOCART score was 54.7 (range 20-85). 12/17 had fill of the defect, 3 had >50% fill; 10 had full border integration and 5/17 were isointense on T2. More than half of patients with greater than 1 post-operative MRI showed a progressive increase in their MOCART score with increasing time since surgery. Average pre-op Lysholm score was 51.99 (SD 15.24, range 29.17-68.76). At an average of 4.8 years post-operatively, the mean Lysholm was 86.37 (SD 10.72, range 70.84-100). This improvement in Lysholm scores was statistically significant, p< 0.001. CONCLUSION: This study clearly shows that this particulated juvenile cartilage transplant procedure has good short term and lasting results. MRI findings confirm that it achieves good ingrowth and integration. In our analysis, there is a trend towards increasing MOCART scores with time, but this did not reach statistical significance. This is the first study that confirms excellent outcomes following DeNovo NT cartilage transplantation in the knee are maintained at a mid-term follow up of nearly 5 years.